4.12 Simple Dispatch: case

The case form dispatches to a clause by matching the result of an expression to the values for the clause:

(case expr   [(datum ...+) expr ...+]   ...)

Each datum will be compared to the result of the first expr using eqv?. Since eqv? doesn’t work on many kinds of values, notably strings and lists, each datum is typically a number, symbol, or boolean.

Multiple datums can be supplied for each clause, and the corresponding expr is evaluated of any of the datums match.

Example:

> (let ([v (random 6)])       (printf "~a\n" v)       (case v         [(0) 'zero]         [(1) 'one]         [(2) 'two]         [(3 4 5) 'many]))

5

'many

The last clause of a case form can use else, just like cond:

Example:

> (case (random 6)       [(0) 'zero]       [(1) 'one]       [(2) 'two]       [else 'many])

'two

For more general pattern matching, use match, which is introduced in Pattern Matching.